1. Field of the Invention:
This invention relates to a cured extruded article of an inorganic hydraulic material reinforced with metal fibers such as iron fibers or stainless steel fibers (hereinafter sometimes referred to as metal fibers), and also a method for production thereof. More particularly, this invention relates to the cured extruded article wherein protrusion of the metal fibers at the extruded surfaces of the article has been substantially prevented by the combined use of the metal fibers and non-metal fibers such as asbestos, carbon fibers, glass fibers, ceramic fibers and plastic fibers (hereinafter sometimes referred to as non-metal fibers), and also a method for production thereof. The cured extruded article normally has satisfactory strength even when the article was coated with a glazing agent and fired.
2. Prior Art:
Hitherto, it has been well known to obtain a molded article of an inorganic hydraulic material by using a mold, which comprises molding, by a method such as casting or pressing, a blend mixture of water, an inorganic hydraulic material such as inorganic cement, calcium silicate or gypsum (hereinafter referred to as inorganic hydraulic materials), and, as necessary, additives such as aggregate (e.g. river sand, gravel, silica sand), water-releasing agents, plasticizers, and expansive agents (hereinafter referred to as additives) into a desired shape. It is known to incorporate either metal fibers or non-metal fibers in such molded articles in order to increase mechanical strength of the resulting molded article (e.g. Japanese Laid-Open Patent Specification No. 4523/1977). It is also known that the above mentioned molded article containing especially about one-inch long metal fibers is increased in its bending strength and the like, and can maintain its initial shape without total fracture when stress is applied to the molded article to form cracks. It is believed, however, to be of no or little value to use both the metal fibers and non-metal fibers because the strength is increased with the metal fibers.
An extrusion method other than the above mentioned molding methods has been employed for molding construction materials, etc. Only non-metal fibers, however, have been actually used as the reinforcing fibers of the extruded articles for the reasons given below.
In the extrusion molding, the fibers are subjected to bending action because a blend mixture is carried by a screw. Immediately after the blend mixture is then extruded from a die and released from the extruding action, the resulting extruded article is subjected to stress acting from its inside to its outside. In this case, the non-metal fibers which were carried and bent are orientated along the flow of the blend mixture when extruded from the die, because non-metal fibers are sufficiently flexible and generally thin in diameter. Thus, in the extrusion molding, the non-metal fibers are completely buried within the extruded article. On the contrary, metal fibers are normally stiff and far thicker in diameter than non-metal fibers because of the process and cost of production. Thus, the metal fibers which were carried and bent can not be orientated straight along the flow of the blend mixture unlike the non-metal fibers. Moreover, the metal fibers can not be satisfactorily buried in the extruded article and are apt to protrude from the extruded surfaces of the article, because of the stress toward the outside of the freshly extruded article. Such extruded articles are not feasible for practical uses and are not so increased in the expected reinforcement effect. In the case of the extruded articles, therefore, only non-metal fibers such as asbestos have been used for such reinforcement.
Incidentally, there might be literature reporting that a blend mixture of an inorganic hydraulic material composition containing metal fibers alone was extruded. Such extruded articles if any are not feasible for practical uses and a lot of the metal fibers must have protruded at the extruded surfaces thereof. Such extruded articles are not on the market as far as known by the present inventors.
Incidentally, it may be possible to cast cement mortar containing both non-metal fibers and especially thin metal fibers in a mold. It is impossible, however, to extrude such cement mortar as explained in detail below.